Swirl helical elements for a viscous impingement particle collection and hydraulic removal system

ABSTRACT

A system and methods for separating liquids, aerosols, and solids from a flowing gas stream whereby gas flows through a helical path formed in a separator element. Partially separated gas exits the bottom of the separator element at a generally conical cavity. Clean gas exits through an inner tube that is axially aligned beneath the helical path. Separated materials exit through an annular space between the inner tube and an outer tube. Separation occurs in the helical channels which include radially diverging walls to provide an aerodynamically efficient flow, in a region of high swirl created in a generally conical cavity beneath the separator element. In higher liquid-loading or slug flow conditions, a passageway may be formed in the separator element for recirculating a portion of the gas flow exiting from the bottom of the outer tube, into an axial passage in the helical separator, and exiting from the bottom of the helical separator near the vertex of the conical cavity.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation-in-part and claims the benefitof U.S. patent application Ser. No. 14/521,141, filed on Oct. 22, 2014,which is a continuation and claims the benefit of U.S. patentapplication Ser. No. 13/250,479, filed on Sep. 30, 2011, entitled “SwirlHelical Elements for a Sub-Micron Viscous Impingement ParticleCollection and Hydraulic Removal System,” all of which are herebyincorporated by reference.

FIELD OF THE INVENTION

The present invention relates in general to systems and methods forremoving liquids and particulate from flowing gas streams. Moreparticularly, the invention relates to systems and methods for removingliquids and particulate from flowing gas streams by encapsulation of theparticulate and impingement separation of the liquid and particulate.Most particularly, the invention related to helical elements generatinghigh swirl forces used to separate liquid and particulate from flowinggas streams.

BACKGROUND

Flowing gas streams often contain particulate material that must beremoved from the gas stream. The particulate material may be anundesirable contaminant in the gas stream. Alternatively, the gas streammay contain a desirable particulate material, for example, in a processfor manufacturing the particulate. Similarly, flowing gas streams maycontain liquids or aerosols, either desirable or undesirable, that mustbe removed from the gas stream.

There presently exist several systems and methods for removingparticulate material and/or liquids from gas streams, includinginertial, viscous, diffusion, filtration, and electrostatic separationsystems and methods. These existing systems for separating solids andliquids from gas streams may be inefficient, pose unnecessaryenvironmental hazards, and may be costly to manufacture and operate.

By way of example, a natural gas transmission company was recentlyexperiencing a problem with its conventional filter separators at acompressor station in Louisiana. Approximately every six weeks, thecompressor station was experiencing harmful slugs of lubrication oilmixed with a black powder. This mixture would coat the filters in thefilter separators and compromise the elements, thus allowing thecontaminated gas to flow through the separator and into the downstreamcompressor equipment. As a result, the compressors had to be shut downfor approximately three days while personnel worked around the clock tomanually change and dispose of the contaminated and potentiallyhazardous filter elements. Further background regarding availablesystems and methods may be found in the applicant's U.S. Pat. No.7,875,103, which is hereby incorporated by reference.

U.S. Pat. No. 7,875,103 discloses a viscous impingement particlecollection and hydraulic removal system. The system solves many of theproblems associated with the prior art by providing a plurality ofhelical separators positioned in a gas flow path and connected through asump to a duplex-filtered side stream. Each helical element is typicallyabout 4 inches in diameter and 5 inches in height, and forms helicalchannels that turn a total about 180 degrees. The channels are formed byparallel fins spaced apart about 0.5625 inch, with an inner radius ofabout 0.28125 inch and short chamfers on the exterior edge of each fin.With typical gas flow rates, this configuration generates centripetalacceleration forces of about 1,300 G's.

Helical elements such as those disclosed in U.S. Pat. No. 7,875,103 aretypically machined from a solid rod of a high grade 4130 chromemolybdenum, 304/316 stainless steel, ceramics, or other suitablematerial depending on the particular flow application. The complexgeometry of the helical channels, inner radius, and fins may alsorequire extensive machining and lengthy processing on a large, five-axisCNC milling machine. Thus, manufacturing each of the 100 or more helicalelements often needed for a single separator may prove costly and timeconsuming.

Accordingly, there exists a need for new systems and methods forremoving particulate and liquids from flowing gas streams wherein thenew systems and methods are capable of effective operation at varyinggas flow rates and potentially high liquid-to-gas weight ratios.Preferably, such systems should also be simpler and less expensive tomanufacture.

SUMMARY

In brief summary, the present invention includes embodiments of systemsand methods for separating and removing liquid and particulate fromflowing gas streams. A flowing gas stream enters a separator vesselhydraulically connected to a waste liquid recovery tank, which may alsobe connected to a duplex-filtered side stream. Optionally, a liquid maybe injected within the separator or upstream from the separator toencapsulate particulate and facilitate separation from the flowing gasstream.

Liquids and particulate separated from the gas stream flow by gravityand inertia into a waste liquid sump. The sump may drain into a wasteliquid recovery tank which may include a duplex-filtered side streamcircuit. The side stream circuit reintroduces filtered liquid back intothe tank so that the filtered liquid may be re-injected in a continuousloop.

The separator may be a vertically oriented helical separator. Coaxialinner and outer tubes provide a flow path for the gas stream and liquidpath open to the sump. The helical separator may be positioned withinand near the top of the outer tube, and includes a plurality of adjacentseparator fins that extend radially outward to form a plurality ofhelical channels. The distance between adjacent fins generally increaseswith the distance from the central axis of the helical element in orderto provide a larger flow path area and increase aerodynamic efficiency.Chamfers may also be provided on a distal vertical edge of the fins anda generally rounded radius may be provided between adjacent fins.

The helical channels may be arranged around the helical separator toform a circular pattern having a diameter larger than the diameter ofthe clean gas tube. The helical channels may turn a total of about 90degrees with a rotational pitch of about 41 degrees and provide a totalchannel area exceeding the area of the inner or clean gas tube. Further,the lower end of the separator may also form a generally conical cavity.Thus, a flowing gas stream may be directed through the helical channelsand exit through the conical cavity to facilitate the generation ofdesirable regions of high swirl that facilitate separation.

The separator may also include a passageway for recirculating a portionof the gas flow from the bottom of the outer tube, into an axial passagein the helical separator, and exiting from the bottom of the helicalseparator near the vertex of the conical cavity. Low pressure near thevertex of the conical cavity facilitates increased flow through theannular space between the inner tube and the outer tube, which, in turn,facilitates the flow of separated liquids in higher liquid-loading orslug flow conditions.

As discussed in more detail below, in comparison to most previousseparator designs, embodiments of the particle collection and hydraulicremoval system of the present invention require simpler and lessfrequent maintenance and cleaning, with fewer operational interruptions,and produces less potentially hazardous waste products.

As is also discussed below, the particle collection and hydraulicremoval system of the present invention provides for a highly efficientgas flow and includes predictable regions of high swirl flow which arevery effective at removing large volumes of liquid and particulate. Theefficient gas flow and predictable regions of high swirl enable the useof a helical design with a scalable geometry which is adaptable to awide variety of gas stream flow rates and particulate/liquid loadingdensities.

Advantageously, the helical elements also require less raw materials andare simpler to manufacture than helical elements employed in existingsystems, while still providing a significant increase in separationefficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and theadvantages thereof, reference is now made to the following briefdescription, taken in connection with the accompanying drawings anddetailed description, wherein like reference numerals represent likeparts.

FIG. 1 is a cross section side view of an embodiment of the particlecollection and hydraulic removal system of the present inventionarranged for separating particulate and liquids from a flowing gasstream.

FIG. 2 is a cut-away side view of an embodiment of a helical separatorof the present invention.

FIG. 3 is a side view of a helical element of the embodiment depicted inFIG. 2.

FIG. 4 is a cross section top view of the embodiment depicted in FIG. 3.

FIG. 5 is a cross section side view along line 5-5 of the embodimentdepicted in FIG. 4.

FIG. 6 is a partial cross section angled view along line 6-6 of theembodiment depicted in FIG. 3.

FIG. 7 is a cut-away side view of the embodiment depicted in FIG. 2showing the location of planes A-E used for CFD analysis.

FIGS. 8 and 9 are a cross section top views of the embodiment depictedin FIG. 4 showing the results of CFD analysis at planes A and E fromFIG. 4.

FIGS. 10 and 11A are cross section side views of the embodiment depictedin FIG. 7, with a portion of the helical element cut away to show theresults of CFD analysis.

FIGS. 11B and 11C are cross section top views along the lines 7 and 8 inFIG. 11A with hidden lines depicting the helical element, and which showthe results of CFD analysis.

FIG. 12 is a chart depicting the results of CFD analysis.

FIG. 13 is a side view of an alternative embodiment of a helicalseparator element.

FIG. 14 is a perspective view of the embodiment from FIG. 13.

FIG. 15 is a top view of the embodiment from FIG. 13.

FIG. 16 is a cut-away side view of the embodiment from FIG. 13.

FIG. 17 is a cut-away side view of an embodiment of a helical separatorusing the helical separator element from FIG. 13.

FIG. 18 is an enlarged cross-section side view of the circled portion inFIG. 17.

DETAILED DESCRIPTION

Particle Collection and Hydraulic Removal System and Method

FIG. 1 illustrates an embodiment of a particle collection and hydraulicremoval system adapted for separating solid particulate and liquids fromflowing gas streams. In general, the system includes a separator vessel100 hydraulically connected to a waste liquid recovery tank 200 and aduplex-filtered side stream 300.

A flowing gas stream 110 may contain particulate and/or liquid that mustbe removed. By way of example, gas stream 110 may be a stream ofpressurized natural gas flowing through a natural gas distributionsystem. For such an application, the particle collection and hydraulicremoval system may be located in or near natural gas compressors,dehydration equipment, glycol contactor towers, or gas measurementequipment. The system may also be employed during pipeline piggingoperations. In this manner, solids and liquids may be removed from thegas stream 110 before it enters the gas compressors or other equipment,where it would otherwise damage or degrade the efficiency of theequipment. In such an application, the particle collection and hydraulicremoval system may optionally include a separator vessel 100 for eachnatural gas compressor, and a waste liquid recovery tank 200 for everytwo separator vessels 100. Those skilled in the art would recognizethat, for this particular application or other similar applications,different combinations of separator vessels 100 and recovery tanks 200may be employed with equal success depending on the various requirementsof the particular application.

In FIG. 1, separator vessel 100 is depicted as a vertically-oblongcylindrical tank, but those skilled in the art would recognize thatvessel 100 may be any closed vertical container with a height sufficientto enclose the internal components, as described more fully below, or aclosed horizontal container with sufficient length to enclose theinternal components (not shown). Vessel 100 includes a gas inlet 120where the flowing gas stream 110 enters the vessel 100. Vessel 100 alsoincludes a gas outlet 140 where the gas stream 110 exits the vesselafter separation of the liquids and particulate.

After gas stream 110 enters at inlet 120, a liquid may be injected intothe gas stream by injector 130, for example, by a plurality of holes ornozzles (not shown) in conduit 274. For these applications, the injectedliquid encapsulates solid particles within the gas stream 110. Mineraloil, compressor lubricating oil, glycol, hydrocarbon condensate, andsimilar liquids may be used as the injection liquid, depending on theparticular requirements of the application. For example, the injectionliquid may be Crystal Plus 70T light viscosity white mineral oilavailable from STE Oil Company, Inc., of San Marcos, Tex.

Vessel 100 also includes a mechanical separator. FIG. 1 depictsseparator 150 located downstream from injector 130 and upstream from gasoutlet 140. Separator 150 is preferably a high-swirl helical separator400 as more fully described in FIGS. 2-6 and the accompanying text.Separator 150 provides for separation of solids, liquids or aerosols,and solids encapsulated within liquids from the gas stream 110.

A second stage of liquid injectors, for example injectors 132, may beemployed downstream from injectors 130 to more fully encapsulateparticulate in the gas stream 110. In FIG. 1, injectors 132 injectliquid directly into the separator 150 through conduit 276.

Solids, liquids, and solids encapsulated within liquids separated fromthe gas stream 110 drop out from the gas stream 110 by gravity andinertia, and fall into sump 160 located at the bottom of vessel 100.During operation, the sump 160 fills with waste liquid until the wasteliquid level activates switch 190. Switch 190 then sends a signal toactuator 182, which opens sump valve 180. Gravity and the internalpressure within vessel 100 may then drain the waste liquid from sump 160through conduits 172 and 184, until the waste liquid level falls belowthe level of switch 191. Switch 191 then sends another signal toactuator 182, which closes sump valve 180. Alternatively, if needed forlow gas stream pressures or for other applications, a sump pump 170 maybe used to pump waste liquid from sump 160. In this manner, a level ofwaste liquid is always maintained in the sump to prevent the escape ofany gasses from gas stream 110 through the sump. Thus, the portions ofthe particle collection and hydraulic removal system downstream from thesump 160 need not be maintained at high internal pressures.

Waste liquid removed from sump 160 then travels through conduits 172 and184, through outlet 210, and into to recovery tank 200. Recovery tank200 collects waste liquid for removal, or for filtering andre-injection. In order to permit re-injection of waste liquid, a sidestream of waste liquid is drained from recovery tank 200 at outlet 220during operation. The waste liquid travels through conduit 302 and intoa side stream filtration system, preferably, a duplex filtration system.

The duplex filtration embodiment depicted in FIG. 1 includes a three-wayvalve 310 which selectively directs waste liquid from recovery tank 200into one of filter vessels 320 and 322. Vessels 320 and 322 preferablyinclude bag-type filter elements or other replaceable filter means thatcan be easily removed and discarded or cleaned. In the preferredembodiment, pump 340 draws waste liquid through a plurality of filterelements (filters 330 or filters 332) in the selected filter vessel(either vessel 320 or vessel 322, respectively). Pump 340 extractsfiltered liquid from the selected filter vessel through conduit 332, andthen pumps the filtered liquid through conduit 342 and into recoverytank 200 at inlet 260. Pump 340 preferably maintains a flow volumethrough side stream 300 which is greater than the flow volume into therecovery tank 200, so that the liquid in recovery tank 200 remains cleanand there is no need for additional mechanisms to segregate clean liquidfrom waste liquid. In a preferred embodiment, pump 340 maintains a flowrate of filtered liquid of at least 5-6 times the flow rate of wasteliquid entering sump 160.

The varying flow rates entering the recovery tank 200 at inlets 210 and260, and exiting the recovery tank 200 at outlets 220 and 261 may causea fluctuation of the liquid level in recovery tank 200. Thus, recoverytank 200 preferably also includes a filter vent 250 or vapor recoverysystem (not shown) to maintain near atmospheric pressure during liquidlevel fluctuations.

After a period of operation, the filters 330 in the currently selectedvessel (filters 330 in vessel 320, or filters 332 in vessel 322) willrequire replacing, which is typically indicated by a higher thanexpected pressure drop. When this occurs, the three-way valve 310 may beswitched to select the other of vessels 320 and 322. The de-selectedvessel may then be opened to simply replace or clean filters 330. Here,the de-selected vessel may be opened to the atmosphere for replacing thefilters without expelling or leaking waste liquid, or exposing personnelto hazardous gasses. Thus, unlike most prior systems, the presentparticle collection and hydraulic removal system need not be bypassed ortaken off line for periodic filter replacement, and personnel need nottake extraordinary environmental precautions to guard against exposureto potentially harmful substances.

Lastly, filtered liquid (e.g., mineral oil) is drawn out from recoverytank 200 at outlet 261 and through conduit 262 by pump 270. Pump 270also delivers filtered liquid through conduits 272, 274, and 276 intovessel 100 for re-injection into the gas stream 110. In this manner,waste liquid is removed from gas stream 110, filtered, and returned forreuse in a substantially continuous closed-circuit.

Helical Separator Element

The mechanical separator 150 illustrated in FIG. 1 is preferably aplurality of tightly-spaced and vertically oriented helical separators,such as the high-swirl helical separator 400 depicted in FIG. 2. Unlikea traditional swirl tube, which uses vanes to force the gas stream toturn and create swirl, embodiments of the present invention use helicalgas flow paths with a geometry chosen to prevent flow separation. Asdiscussed below, the cross-section of the helical gas flow paths, theirturning angle, and their axial pitch all cooperate to generate swirlwithout a loss of aerodynamic efficiency. In addition to being acentrifugal type separator, embodiments of the present invention arealso an impingement type separator. As liquids enter the helical gasflow path, liquid aerosols impinge and coalesce on the walls of the flowpaths. This aerodynamically efficient flow tends to retain the impingedliquids on the walls of the channels, forming a film that helps toimprove the separation efficiency.

In FIG. 2, helical separator 400 includes helical element 410 securedwithin and at the top of a generally cylindrical outer; tube 420.Generally cylindrical inner tube 430 has a smaller outer diameter thaninner diameter of outer tube 420, and is vertically spaced a shortdistance below helical element 410, for example, 2 inches below helicalelement 410. The lower portion of inner tube 430 is retained andcentralized within outer tube 420 in part by vertically oriented fins440.

In FIG. 2, the flow direction of gas stream 110 (also depicted inFIG. 1) is generally illustrated with arrow F. The gas stream 110 isdirected into the top of helical element 410, which is surrounded byouter tube 420. A plurality of channels 460 and diverging fins 470(better illustrated in FIG. 4) are formed in a circular pattern aroundthe exterior of helical element 410. The channels 460 and diverging fins470 wind clockwise from the top to the bottom of helical element 410and, when surrounded by outer tube 420, form a plurality of helical gasflow paths.

As the gas stream 110 flows downwardly through the helical flow pathprovided by channels 460, fins 470, and outer tube 420, the gas stream110 impinges on the walls 472 of fins 470 and the inner walls of outertube 420, and begins to rotate clockwise (as seen from above).Particulate and liquids carried within the gas stream 110 have greaterdensity than the gas stream 110, and a corresponding higher kineticenergy. As discussed in more detail below, the helical gas flow pathformed by channels 460, fins 470, and outer tube 420 provides a highlyefficient gas flow with roughly equal axial and tangential velocitycomponents. Thus, particulate carried within the gas stream 110 impingeson the interior surface of channels 460, fins 470, and outer tube 420,and becomes further encapsulated within the liquid. Liquid vapor andsmaller liquid droplets in the gas stream 110 likewise impinge on thewalls of the helical flow path and coalesce to form larger liquiddroplets and liquid streams or sheet flow, particularly on the lowermostwalls of fins 470.

Similarly, when the gas stream 110 begins to rotate clockwise in thehelical flow path, the increased angular velocity of the gas stream 110creates centrifugal forces. The centrifugal forces have a greater effecton the particulate and liquids in the gas stream 110, thereby causingcoalescence and encapsulation on the inside wall of outer tube 420.Thus, coalescing liquid droplets, liquid streams, and encapsulatedparticulate form larger liquid streams flowing in sheet flow downwardlyalong the walls of fins 470 and along the inside wall of outer tube 420.The sheet flow traveling downwardly along the inside wall of outer tube420 continues flowing downwardly to the bottom of outer tube 420, whereit flows into the annular space formed between the outer tube 420 andthe inner tube 430, and then into the sump 160 (depicted in FIG. 1). Anysheet flow remaining on the walls of fins 470 exits the bottom ofhelical element 410 and also preferably flows into the sump 160.

As discussed in more detail below, a preferred configuration of helicalelement 410 is about 4 inches in diameter and 2.5 inches high, with 8channels 460 and 8 diverging fins 470 that turn a total of about 90degrees. Thus, the height of the helical element 410 is about 62.5percent of its diameter. The walls of fins 470 preferably diverge fromthe central axis of the helical element 410 to form an angle α of about22 degrees. This provides a larger width between adjacent distal ends offins 470 and a greater cross-sectional area for the helical flow path.With typical gas flow rates, this configuration generates centripetalacceleration forces of about 6,800 G's with a Reynolds number in therange of 0.68×10⁴ to 4.4×10⁴.

As indicated by the flow arrow V in FIG. 6, the gas stream 110 flowingthrough helical element 410 also forms a secondary vortex rotatingclockwise when viewed generally from the top along line 6-6 (FIG. 3).Embodiments of the present invention are adapted to address thesevortices in order to facilitate impingement separation specifically nearthe inner wall of outer tube 420, where liquids exiting the bottom ofhelical element 410 are more likely to flow into the sump. Theseembodiments are also adapted to minimize any disruption of the vorticesnear the surface of channel 460, and thereby minimize the risk thatliquids may become re-entrained upon exiting the bottom of helicalelement 410.

A preferred embodiment includes several means to address these secondaryvortices and prevent liquid re-entrainment. As shown in FIGS. 4-6, theintersection of the channels 460 and the walls 472 of fins 470 forms agenerally semi-circular, interior radius 465. In a preferredconfiguration, the radius 465 may be about 0.2817 inch. The radius 465inhibits liquid separation in the secondary vortices on what wouldotherwise be square corners formed at the intersection of the channels460 and the walls 472 of fins 470.

Additionally, relatively small chamfers 475 are formed along thevertical exterior edges of fins 470. In a preferred configuration,chamfers 475 may be formed at an angle β of about 34 degrees measuredfrom the walls of fins 470, and have a length of about 0.0992 inch. Whenhelical element 410 is fitted tightly within outer tube 420, thechamfers 475 form small pockets that act as additional vane-typeseparators oriented to remove liquids and particulate from the secondaryvortices. In this manner, coalesced liquid streams are more effectivelydirected away from channels 460 and are trapped in a vertical pocketformed between the chamfers 475 and the inner wall of outer tube 420.The liquid streams flowing downwardly along the inner wall of outer tube420 are also thereby less prone to re-entrainment within the gas stream110. The use of chamfers 475 has been shown to significantly increasethe effective liquid removal rate over non-chamfered edges under typicalconditions.

In a preferred configuration including chamfers 475, the straightportion of the walls of fins 470 is approximately 0.5 inch in length andthe radius 465 is located at a distance D_(r) of about 1.1875 inchesfrom the central axis of the helical element 410. Thus, the channels 460are disposed radially in a circular pattern having a diameter of 2.375.Consequently, gas flow exits the bottom of helical element 410 at aradius larger than that of the opening for clean gas provided by innertube 430, which typically has a diameter of slightly less than twoinches and a radius of slightly less than one inch. It is believed thatthis configuration significantly increases the separation efficiency ofhelical elements 410.

This preferred geometric configuration of helical element 410 alsoprovides a total open area of each channel 460 of about 0.4867 squareinch. For 8 channels as typically used on a 4 inch diameter helicalelement 410, this provides a total gas flow path area of about 3.8936square inches. By comparison, a typical 2 inch diameter inner tube 430provides an open area for clean gas flowing through the system of about2.95 square inches.

Thus, it has been found that using fins 470 with walls that divergeradially from the central axis of the helical element 410 provides for acombined flow path area through helical element 410 which exceeds theflow path area for clean gas through the inner tube 430. It is believedthat radially diverging walls 470, which help provide this larger flowpath area without locating the radius 465 inside the diameter of theinner tube 430, contributes significantly to the aerodynamicallyefficient flow observed through helical separator 410.

The radius, turning angle and cross-section of the helical gas flowpaths also provide a rotational pitch angle ρ (FIG. 3) which contributesto the aerodynamic efficiency of gas flow through the helical element410. Here, the rotational pitch angle ρ is very similar to what iscommonly referred to as the “helix angle,” which is typically determinedby taking the inverse tangent of the quotient of the mean helicalcircumference divided by the helix lead (the axial distance required forone complete helical rotation), i.e.:Helix angle=tan⁻¹(2·π·r _(m)/lead), where r _(m) is the mean radius ofthe helix.

However, because embodiments of the present invention may use a morecomplex helical channel cross-section, the calculation of rotationalpitch angle ρ is simplified by using the radius measured from thecentroid of helical element 410 to the center of rounded radius 465(FIG. 6), as opposed to the “mean” radius. Here, helical channels 460using the cross-section geometry discussed above, which turn 90 degreesin 2.5 inches (or 360 degrees in 10 inches), provide a rotational pitchangle ρ of about 41 degrees. Stated differently, helical channels 460that turn 90 degrees with a rotational pitch angle ρ of about 41 degreesrequire that the height of the helical element 410 be about 2.5 inches.

As discussed in more detail below, this geometric configuration of thehelical gas flow path provides for a gas flow with roughly equal axialand tangential velocities. In turn, this contributes to a flow patternthrough helical element 410 with very similar velocity, pressure, andswirl patterns throughout the length of channels 460. This provides forvery predictable flow characteristics and contributes to high separationefficiencies throughout a wide range of gas flow rates.

The spiraling of the gas caused by the geometry of the helical gas flowpath creates a leading and trailing edge at the helical inlet, therebycreating different inlet conditions for two counter rotating vortexlegs. This creates an inlet vortex condition typically associated withirrotational flow. However, the trailing vortex rotates opposite of theinlet vortex. The opposite rotation of these two vortices forces allcontaminants towards the walls of the helical gas flow path. Thiscreates a sheet of liquid on the walls that will entrap small aerosolsand carry them to the outlet of the helical gas flow path.

However, a trailing vortex is also formed at a small distance below thehelical gas passage inlet and travels opposite of the process gas flow.In order for the trailing vortex to exist, the gas following the processflow path must change direction. This abrupt change in directionenhances separation by abruptly changing the flow direction and causingdisengagement.

As shown in FIG. 5, helical element 410 also includes an interiorconical cavity 495 formed at the bottom end of helical element 410. Thesurface of the cavity 495 generally forms a 45 degree angle to thecentral axis of helical element 410. The tip of the conical cavity 495may be truncated so that the cavity 495 extends axially about 1.5 inchesinto the bottom of helical element 410. When liquid streams flowing inchannels 460 and along the walls of fins 470 exit the bottom of helicalelement 410, the liquid streams tend to exit at a tangent to the bottomsurface of helical element 410. Conical cavity 495 acts to direct theseexiting liquid streams perpendicularly to the surface of the cavity andtoward the interior surface of outer tube 420, as indicated by the flowarrows in FIG. 5. As discussed in connection with the CFD analysisbelow, the geometry, spacing, and area of the helical channels 460,radially diverging fins 470, cavity 495, and inner tube 430 act tocreate regions of high swirl directly beneath the helical element 410.In addition, toroidal vortices formed in the annular space between innertube 430 and outer tube 420 act to maintain sheet flow along theinterior surface of outer tube 420. Vertical fins 440 act to disrupt anyremaining gas vortices within the annular space formed between outertube 420 and inner tube 430, and thereby further prevent or reduceliquid re-entrainment.

Inner tube 430 may also include a small rim lip 450 at the top endfacing the bottom of helical element 410, and a recessed channel 455formed below the rim lip 450. Vortices and gas flow within the annularspace formed between outer tube 420 and inner tube 430 may cause a sheetflow of liquid on the exterior of inner tube 430. This sheet flow mayundesirably creep upward against the force of gravity. The recessedchannel 455 and rim lip 450 disrupt this creeping flow and prevent itfrom passing over the top rim of inner tube 430, where the creeping flowmight otherwise be re-entrained within the gas stream 110.

CFD Analysis of the Helical Separator Element

An analysis using computational fluid dynamics (CFD) was performed usinga model of an exemplary embodiment of the helical separator element 410as shown in FIGS. 2-6 and described above. A mesh of 750,000 elementswas used with smaller mesh elements located inside the helical channelflow path and in the concave conical cavity 495 near the bottom of thehelical element 410. A larger mesh size was employed inside the innertube 430 and in the annular space formed between the outer tube 420 andinner tube 430. A gas flow of air was simulated under steady conditionsat standard temperature and pressure (STP) at flow rates of 1.567,3.917, 6.267, 8.617, and 10.967 pounds per minute. The analysis used arealizable k-ε turbulence model to capture swirling flow with asecond-order differencing scheme.

The analysis examined velocity, pressure, and flow lines at horizontalplanes A, B, C, D, and E shown by dashed lines in FIG. 7. Planes A-Ewere located at the upstream entrance of the helical flow path, at halfway between the entrance and the exit at cavity 495, at the exit atcavity 495, half way between the exit and the top of inner tube 430, andat the top of inner tube 430. Results are summarized below.

The analysis first examined velocity vectors in the planes A-E. Velocityvectors in the plane A immediately above the entrance to separatorelements 420 were shown to gradually increase to a concentration nearpoint 510 shown in FIG. 8. Velocity vectors in the plane A just insidethe entrance to separator elements 420 increased to a concentration nearpoint 520. While the general magnitude of velocity vectors increasedwith higher flow rates, the overall pattern of velocity vectors remainednearly unchanged.

Similarly, velocity vectors in the plane B half way between the entranceand exit of separator elements 420 were shown to more dramaticallyincrease, with higher velocities becoming more concentrated near point520. Again, the pattern of velocity vectors remained nearly unchangedwith increases in flow rate (with the general magnitude increasing withhigher flow rates). As indicated by point 520, velocities were highertoward the trailing surface of the channels 460 and lower toward theleading surface. The analysis indicated that the helical flow pathformed by channels 460, diverging fins 470, and outer tube 420established an aerodynamically efficient flow at all gas flowvelocities, without the presence of flow separation or flow reversal.

CFD analysis also showed that velocity vectors in the plane C at theexit of channels 460 on the surface of cavity 495 formed a dramaticswirling vortex core indicated with velocity vectors 530 on the insideof cavity 495. Velocity vectors in the plane D half way between the exitand the entrance to inner tube 430 showed a similar swirling vortex corepattern, but expanded radially toward the outer tube 420. As before,with varying flow rates, the peak velocity generally increased, but thevelocity patterns at each respective plane C and D remained nearlyunchanged.

As shown in FIG. 9, velocity vectors in the plane E at the top of innertube 430 (indicated with velocity vectors 540) show that the high swirlregion migrated from inside the cavity 495 to occupy the annular spacebetween the inner tube 430 and the outer tube 420. Although not depictedin FIG. 9, a region of much lower velocity swirling flow was also shownon the inside of inner tube 430. Again, the swirling flow velocitygenerally increased with the flow rate, but the direction of swirlingflow vectors generally remained the same at all flow rates.

Much like the consistent flow vectors observed for varying flow rates ateach of the horizontal planes A-E, pressure contours on a vertical planethrough the center of the helical separator 400 had a very similardistribution at varying flow rates, with only peak pressures increasingwith an increased flow rate. As shown in FIG. 10, vortices 550 formed inthe cavity 495 at the bottom of helical element 410, and toroidalvortices 560 formed in the annular space between the inner tube 430 andthe outer tube 420. The pattern of pressure contours in the verticalplane also remained nearly constant for all flow rates used in themodel.

It is believed that the toroidal vortices 560 greatly enhance separationefficiency. The gas flowing near the boundary layer on the inside ofouter tube 420 travels below the clean gas inlet, i.e., below the lip450 shown in FIG. 2. This is due to the inertial forces acting on thegas molecules. The gas will continue to travel below the inlet of innertube 430 until the force created by the low pressures closer to theoutlet at fins 440 is larger than the inertial force pushing the gasdown. Once this occurs, the gas changes direction and travels upwardsalong the outside of the inner tube 430. As the gas reaches the innertube 430, it forms two path lines: one entering the clean gas tube andthe other returning to the boundary layer on the inside surface of outertube 420. As the gas returns to the boundary layer, the path lines formclosed loops and produce a donut-shaped region of vorticity that may bereferred to as a toroidal vortex ring.

CFD analysis showed that this toroidal vortex ring generates a downwardflow along the inner surface of the outer tube 420 and an upward flowalong outer surface of the inner tube 420. When the liquids, aerosols,or particulate are pushed toward the outer tube 420 in the swirl region,inertial forces push them toward the toroidal vortex. The toroidalvortex pushes the material down into the annular space between the innertube 430 and outer tube 420. When the lower pressure beneath the inletof inner tube 430 overcomes the inertial force, the gas will changedirection sharply and flow upward along the outside of inner tube 430.This sharp change in direction causes the liquid, aerosols, andparticulate in the toroidal vortex to disengage from the gas stream andflow into the sump 160 (FIG. 1).

The CFD model more closely examined this swirling flow throughout thedevice by computing the swirl angle in both the vertical plane (asgenerally illustrated in FIG. 10), and in the horizontal planes A-Eillustrated in FIGS. 7-9. Here, the swirl angle was defined as thearc-tangent of the ratio of the tangential flow velocity divided by theaxial flow velocity. Thus, a swirl angle approaching 90 degrees wouldindicate a predominantly tangential flow and negligible axial flow, aswirl angle approaching 0 degrees would indicate a predominantly axialflow, and a swirl angle of 45 degrees would indicate equal tangentialand axial flow velocities. As shown in FIGS. 11A and 11B, an area 570 ofhigh swirl angle approaching 90 degrees was shown in the cavity 495, andas shown in FIGS. 11A and 11C, another area 580 of high swirl angleapproaching 90 degrees was shown in the annular space between the top ofthe inner tube 430 and the outer tube 420. An area 590 of high swirlvelocity (tangential flow velocity) was shown in the region between thebottom of cavity 495 and near the top of inner tube 430. Although notshown in FIG. 11, the swirl angle remained relatively constant at about45 degrees throughout the helical passages, indicating anaerodynamically efficient flow. The swirl angle pattern and swirlvelocity pattern were both nearly the same at all flow rates, withhigher velocities at higher flow rates.

Using the results above, the model also examined the relationshipbetween mass flow rate and flow velocity (both axial and swirlcomponents) at planes A-E in the helical separator (shown in FIG. 7).The chart in FIG. 12 depicts the maximum velocities calculated atdifferent flow rates normalized by the velocities calculated at thelowest mass flow rate of 1.567 pounds per minute. As shown in FIG. 12,each of the velocities (velocity at the entrance to the helical element410, velocity inside helical element 410, velocity at exit of helicalelement 410, velocity in the space between the helical element 410 andthe inner tube 430, and velocity at the entrance to the inner tube 430)vary almost linearly with mass flow rate. The analysis thus indicatesthat the helical separator design is highly scalable, and maintainsdesirable aerodynamic characteristics for widely varying flow rates.

As noted, the CFD model indicates that a high degree of swirl exists inthe space between the helical element 410 and the top of inner tube 430.Particles and/or liquid droplets in this region are pushed radiallyoutwards by the action of centrifugal force associated with the swirlingflow. As the particles and/or droplets migrate radially outward, theswirl velocity decreases and the swirl angle increases, creating aregion dominated by swirl flow with negligible or very small axial flow.Any liquid, aerosols, or particulate in this region are forced bycentrifugal force outward toward the surface of outer tube 420, wherethe downward axial component of the toroidal vortex (e.g., 560 in FIG.10) causes the particles to drift into the annular space, therebyseparating the particles and/or droplets from the gas.

Where it was previously thought that high G forces beyond 6,000 G'swould impede separation, the swirling flow created by embodiments of thepresent invention suggest the presence of an efficient flow facilitatingseparation at well beyond 6,000 G's (e.g., 6,800 G's for a mass flowrate of 10.967 pounds per minute). These high centrifugal forces make itpractically impossible for any liquid, aerosols, or particulateentrained in the gas flow, even at very small sizes, to avoid separationand collection in the annular space formed between inner tube 430 andouter tube 420.

Test Results

A single, full scale helical separator 400 including helical element 410was tested in a closed system to determine its effectiveness. Testresults were compared to the results achieved under the same conditionsusing the helical separator and helical element as disclosed in U.S.Pat. No. 7,875,103 (hereinafter “the '103 separator”). Tests wereperformed using a flow of air supplied by a blower and with threedifferent entrained liquids: 75 weight lubricating oil, propyleneglycol, and water. The liquid flow remained constant. Lubricating oilwas supplied at 0.1 pounds per minute, glycol anti-freeze at 0.25 poundsper minute, and water at 16 pounds per minute. The separationcharacteristics of each device were observed at increasing air supplyvelocities in the range of 4,000 to 7,600 feet per minute.

For the tests performed with oil and glycol as the entrained liquid, thepresence of any liquid carried into the clean gas tube (e.g., inner tube430 in FIG. 2) within 30 minutes of operation indicated that thesupplied air velocity exceeded the maximum flow rate for the respectivedevice. Conversely, the absence of any oil or glycol carried into theclean gas tube after 30 minutes of continuous operation indicated thatthe device effectively separated the air and liquid. For the testsperformed with water as the entrained liquid, limitations of the testequipment (i.e., maximum blower air velocity and liquid sump capacity)allowed only five minute of operation. At the effective limits of thetest equipment (7,200 feet per minute air velocity), both deviceseffectively separated all water from the air flow for a period of 5minutes, even at 16 pounds of water per minute, at which time the testshad to be terminated because the separated water completely filled the10 gallon sump. For this reason, the experiment was not capable oftesting the effective limits of separating water from air for eitherdevice.

Table 1 below shows the maximum effective air velocity for each of thetested separators (the '103 separator and an embodiment of the presentinvention) at the indicated liquid flow rates. In sum, results of thistesting suggest that the embodiment of the present invention is about7-15 percent more efficient than the device disclosed in U.S. Pat. No.7,875,103.

Liquid ′103 Separator Embodiment Increase (%) 75w Oil (0.1 lb/min.)4,800 5,500 14.6 Glycol (0.25 lb/min.) 4,500 4,800 6.7 Water (16lb/min.) 7,200 7,200 —

Not only was this embodiment found to be more efficient at highliquid-to-gas weight ratios and varying gas flow rates than the helicalseparator disclosed in U.S. Pat. No. 7,875,103, but the helical elementsof the present invention are also much smaller, require less rawmaterials, and require less time to manufacture. By comparison, thehelical elements of the present invention are typically at least 25percent less expensive than those described in U.S. Pat. No. 7,875,103.Considering that many applications require 100 or more helical elements,the potential cost savings and reduced manufacturing time may besignificant.

Another embodiment of a separator is illustrated in FIGS. 13-18. Asnoted previously in connection with the embodiments illustrated in FIGS.2-7, liquid streams generally flow along on the walls of the annularspace formed between the inside wall of the outer tube 420 and theoutside wall of the inner tube 430, and then into the sump 160. Thepresent embodiment illustrated in FIGS. 13-18 recirculates a portion ofthe gas stream exiting near the bottom of outer tube 720, through thespace 152 formed between adjacent helical separators (shown in FIG. 1),then back into the helical element 610, through a transverse bore 620and an axial bore 630, and, finally, out from the bottom of helicalelement 610 near the vertex of conical cavity 795. This recirculation iscaused chiefly by the pressure differential existing between the extremelow pressure near the vertex of conical cavity 495 and the higherpressure in the space 152 formed between adjacent helical separators.

In order to create a path for the recirculation of gas flow, one or moretransverse bores 620 and an interconnected axial bore 630 may be formedin the helical element 610. The resulting passageway formed by bores 620and 630 provides a recirculating gas flow path R (shown in FIG. 17)between the bottom of the annular space formed between the outer tube720 and the inner tube 730, and the opening of axial bore 630 near thevertex of conical cavity 695. The recirculating gas flow path R isgenerated by a very low pressure region near the vertex of conicalcavity 695. This low pressure region is created by vortices in theconical cavity 695, such as discussed above in connection with vortices550 from FIG. 10 and the accompanying text.

In order to accommodate the transverse bores 620 without interruptingthe gas flow path in the helical channels 660, the top portion ofseparator 610 may form a generally conical shape 615 best illustrated inFIG. 13. Transverse bores 620 may be formed in this conical shape 615upstream from the start of helical channels 660. Transverse tubes 760extend through outer tube 720 and connect to transverse bores 620. Inthis manner, the recirculating gas flow path R is largely unaffected bythe upstream gas flow entering the helical separator 610, and does notinterfere with the separation of liquid and particulate from the flowinggas stream.

The helical element 610 in the present embodiment is generally ahalf-scale version of the helical element 410 illustrated in FIGS. 2-7.For example, the outer diameter of the helical element 610 may be 2inches, and its overall height may be 2.125 inches. The helical element610 also differs from the previous embodiments by forming a conicalshape 615 and including transverse bores 620 and an axial bore 630. Theconical shape 615 forms a 35 degree cone extending from the upstream endfor approximately 1.375 inches along the axis of helical element 610.Helical channels 660 may form an angle α of about 22 degrees(illustrated in FIG. 6 with respect to the previous embodiments). Thehelical channels extend from the bottom of the helical element 610 andterminate against the conical shape 615 at a height of about 1.66inches. The cross-sectional area of each channel (A_(h) in FIG. 15) isapproximately 0.1402 square inches, which provides a totalcross-sectional area for all eight channels 660 of about 1.1216 squareinches.

Transverse bores 620 may have an inside diameter of approximately 0.3390inches, and axial bore 630 may have an inside diameter of approximately0.25 inches. In this embodiment, outer tube 720 has an inside diameterof about 2 inches, and inner tube 730 has an inside diameter of about0.75 inches and a cross-sectional area (A_(t) in FIG. 17) of about 0.442square inches. Inner tube 730 may be spaced apart from the bottom ofhelical element 610 by about 3.9375 inches.

In the previous embodiments described in connection with FIGS. 2-7,inner tube 430 formed a small rim lip 450 at the top end to inhibit anysheet flow of liquid from creeping upward and over the top of inner tube430. In the present embodiment, the recirculation of gas flow tends toinhibit this sheet flow. Thus, the upper end of inner tube 730 need notemploy a rim lip. Instead, as shown in FIG. 18, the upper end of innertube 730 may have a smooth exterior surface and rounded interior surface750.

In comparison to the previous embodiments, the recirculating gas flowpath R created in the present embodiment tends to bias flow toward theannular space near the bottom of outer tube 720. This biased flow tendsto clear any high liquid loading or slug flow passing through thehelical separator 700 of the present embodiment more effectively thanthe embodiments illustrated in FIGS. 2-7. Thus, the present embodimentmay be more suitable to applications wherein high liquid loading orfrequent slug flow may be expected.

While various system and method embodiments have been shown anddescribed herein, it should be understood that the disclosed systems andmethods may be embodied in many other specific forms without departingfrom the spirit or scope of the invention. The present examples are tobe considered as illustrative and not restrictive. The intention is notto be limited to the details given herein, but may be modified withinthe scope of the appended claims along with their full scope ofequivalents.

What is claimed is:
 1. A system for particle collection and hydraulicremoval comprising: a separator vessel with a gas stream inlet, a gasstream outlet, and forming a space therein; a vertically oriented outertube with a top and a bottom positioned within the space in the vessel;a generally cylindrical separator element disposed within and near thetop of the outer tube, the separator element having a central axis andforming a generally conical shape at an upstream end, and forming agenerally conical cavity at the bottom surface thereof; a verticallyoriented inner tube axially aligned within the outer tube and axiallyspaced apart beneath the separator element, the inner and outer tubesforming an annular space therebetween; a plurality of helical gas flowpaths formed by radially diverging fins extending from the separatorelement; such that the annular space forms a flow path for liquid orparticulate separated from the gas, and the inner tube forms a flow pathfor gas separated from the liquid or particulate; and a recirculatinggas flow path extending from the downstream end of the annular space,through the space in the vessel, into a transverse passageway formed bya conduit extending from a hole in the outer tube to a transverse borein the conical shape, into an axial passageway in the separator element,and exiting near the vertex of the conical cavity.
 2. The system ofclaim 1 wherein the transverse passageway and the axial passageway areboth closed to an upstream gas stream entering the system.
 3. The systemof claim 1 wherein the transverse passageway is generally perpendicularto the axial passageway.
 4. The system of claim 2 wherein the transversepassageway is upstream from the helical gas flow paths.
 5. The system ofclaim 2 further comprising: a waste liquid sump at the bottom of thevessel; a waste liquid recovery tank hydraulically connected to thewaste liquid sump; wherein the outer tube is above the sump; such thatliquid or particulate separated from the gas flows to the sump, and gasseparated from the liquid or particulate flows from the inner tube tothe gas stream outlet.
 6. A system for particle collection and hydraulicremoval comprising: a separator vessel with a gas stream inlet, a gasstream outlet, and forming a space therein; a vertically oriented outertube with a top and a bottom positioned within the space in the vessel;a generally cylindrical separator element disposed within and near thetop of the outer tube, the separator element having a central axis andforming a generally conical shape at an upstream end, and forming agenerally conical cavity at the bottom surface thereof; a verticallyoriented inner tube axially aligned within the outer tube and axiallyspaced apart beneath the separator element, the inner and outer tubesforming an annular space therebetween; a plurality of helical gas flowpaths formed by radially diverging fins extending from the separatorelement, and a rounded radius in the separator element between adjacentfins; such that the annular space forms a flow path for liquid orparticulate separated from the gas, and the inner tube forms a flow pathfor gas separated from the liquid or particulate; and a recirculatinggas flow path extending from the downstream end of the annular space,through the space in the vessel, into a transverse passageway formed bya conduit extending from a hole in the outer tube to a transverse borein the conical shape, into an axial passageway in the separator element,and exiting near the vertex of the conical cavity.
 7. The system ofclaim 6 wherein: the helical gas flow paths have a generally bell-shapedcross section; and the transverse passageway and the axial passagewayare both closed to an upstream gas stream entering the system.
 8. Thesystem of claim 7 wherein the helical gas flow paths have a combinedcross-sectional area that exceeds the open cross-sectional area of theinner tube.
 9. The system of claim 7 further comprising: a waste liquidsump at the bottom of the vessel; a waste liquid recovery tankhydraulically connected to the waste liquid sump; wherein the outer tubeis above the sump; such that liquid or particulate separated from thegas flows to the sump, and gas separated from the liquid or particulateflows from the inner tube to the gas stream outlet.
 10. The system ofclaim 6 further comprising: a waste liquid sump at the bottom of thevessel; a waste liquid recovery tank hydraulically connected to thewaste liquid sump; wherein the outer tube is above the sump; such thatliquid or particulate separated from the gas flows to the sump, and gasseparated from the liquid or particulate flows from the inner tube tothe gas stream outlet.